Vinyl chloride polymers, with hard as well as soft characteristics, are being increasingly utilized as building components in buildings and conduits, as well as in fabrics, upholsteries, and wall coverings. Because of these uses, there is a need that these materials be subjected to treatments to improve their fire-retarding characteristics as well as for reducing the amount of smoke evolved in the event of a fire. A large number of additives have been suggested, which are incorporated into polyvinyl chloride for this purpose. However, very few of the materials suggested have proven to be satisfactory. Many of the additive compounds are incompatible with polyvinyl chloride, i.e., are hard to incorporate, and result in intense discolorations of the polyvinyl chloride, or adversely affect the physical properties of the polyvinyl chloride.
Often the smoke-reducing properties of the additive are only apparent properties because the additive actually functions only as a flame retardant which in turn reduces the amount of smoke evolved. More specifically, when this type of additive is tested, in polyvinyl chloride usually under the testing conditions of an NBS smoke chamber, one of the most widely used standard methods for determining smoke density, the amount of smoke evolved under flaming conditions is lower than that evolved under smoldering conditions. Actual smoke reduction under smoldering conditions is observed only rarely; however, one should expect this property from a true smoke-reducing additive.
The prior art teaches that various copper compounds, alone or in mixtures with other metallic compounds, are effective smoke-reducing additives. U.S. Pat. No. 3,845,001 teaches the use of Cu.sub.2 O alone, or in mixtures with MoO.sub.3 or Fe powder. According to U.S. Pat. No. 3,903,028, Cu.sub.2 O is employed in combination with Fe.sub.2 O.sub.3. However, all of these compounds result in a considerable discoloration of the polymers. The prior art also teaches the use of copper salts in the form of carboxylates or, for example, acetylacetonate, but these substances are also unsuitable due to the decomposition of the compounds at the incorporation temperatures, and because of the discoloration connected therewith. DOS No. [German Unexamined Laid-Open Application] 2,700,656 suggests the use of copper oxalate as the smoke-reducing additive. The copper oxalate is incorporated in this case at a temperature of 163.degree. C., and the polymer is press-molded into panels at 177.degree. C. However, at the usually higher incorporation temperatures of about 190.degree.-200.degree. C., the use of copper oxalate also results in significant discoloration toward a blue-gray color.